Field of the Invention
The present invention relates to a scanning-line drive circuit used in an electro-optical device such as an image display device and an imaging device, and particularly to a scanning-line drive circuit configured with only field effect transistors of the same conductivity type.
Description of the Background Art
An electro-optical device including a scanning-line drive circuit connected to a scanning line and scanning pixels is widely known. For example, in an image display device (hereinafter, referred to as a “display device”) such as a liquid crystal display device, a gate line (scanning line) is provided for each of pixel lines of a display element (display panel) having a plurality of pixels arranged in lines and columns (in a matrix), and the gate lines are sequentially selected and driven in the cycle of one horizontal period of a display signal, to thereby update a display image. As a gate-line drive circuit (scanning-line drive circuit) for sequentially selecting and driving the pixel lines, that is, the gate lines, there may be adopted a shift register which performs shifting whose one-round operation is made in a one-frame period of the display signal.
Pixels of an imaging element used in an imaging device are also arranged in a matrix, and these pixels are scanned by a gate-line drive circuit to thereby extract data of a captured image. A shift register may be adopted as a gate-line drive circuit of the imaging device, too.
A shift register serving as a gate-line drive circuit includes a plurality of cascade-connected shift register circuits provided for each one of the pixel lines, that is, each one of the gate lines. In this specification, each of the plurality of shift register circuits included in the gate-line drive circuit is called a “unit shift register”. Thus, an output terminal of each individual unit shift register included in the gate-line drive circuit is connected to a corresponding gate line, and moreover connected to an input terminal of the next-stage or the subsequent-stage unit shift register.
It is desirable that the shift register used in the gate-line drive circuit is configured with only field effect transistors of the same display device, in order to reduce the number of steps of the manufacturing process for a cost reduction.
The gate-line drive circuit is operated so as to sequentially select the gate lines by transmitting a start pulse inputted the unit shift register of the most preceding stage to the subsequent-stage unit shift registers one after another. The start pulse is a signal (external signal) supplied from the outside of the gate-line drive circuit, and generated by a start pulse generation circuit which is formed on a substrate different from a substrate on which the gate-line drive circuit is formed.
However, an increase in the number of external signals causes an increase in the number of necessary circuits such as a circuit for generating the external signal and a level shifter for adjusting the level of the external signal. This may be a factor in a cost increase of the device. Accordingly, in order to reduce the manufacturing cost of an electro-optical device, it is preferable to reduce the number of external signals as small as possible. For this purpose, there has been made an attempt to reduce the number of external signals by providing the start pulse generation circuit on the same substrate as the gate-line drive circuit is provided to thereby eliminate the need to supply the start pulse from the outside (for example, Japanese Patent Application Laid-Open No. 2006-269002; and Specification of United States Patent Application Publication No. 2008/0122774).
The number of external signals can be reduced, by providing the start pulse generation circuit and the gate-line drive circuit on the same substrate as disclosed in Japanese Patent Application Laid-Open No. 2006-269002 and Specification of United States Patent Application Publication No. 2008/0122774. However, as a matter of course, it is necessary that the area for forming the start pulse generation circuit is ensured on the substrate. From the viewpoint of the manufacturing cost, it is preferable that the substrate has a small area.